Many devices, such as motors, amplifiers, and the back lights that power liquid crystal displays are supplied power through an arrangement of four mosfets. The arrangement is generally known as a full bridge or an H-bridge. A control circuit for the full bridge will include an oscillator and pulse width modulator for generating gate control signals. The outputs of the control circuit are coupled to gate drivers to boost the voltage of the gate control signal to a level acceptable to the mosfets. The gate drivers may also provide isolation of the mosfets from noise generated by the oscillator in the control circuit.
The control circuit and the gate drivers may themselves be integrated into a single circuit and packaged in one or more small size packages, such as a molded leadless package. Such packages consume a small area and a small volume. However, each mosfet is as large as or larger in size than the control circuit. The mosfets can be individually packaged and wired to the control circuit on the printed circuit board of the controlled system. However, four separate mosfets consume a lot of area and volume. As systems shrink, the amount of area and volume for control and mosfet packages is also reduced.
In order to address the problem of fitting more devices into ever-smaller spaces and improving the thermal and electrical performance of packaged devices, those skilled in the art have packaged four mosfets together in a single package. A typical full bridge mosfet package has two high side mosfets and two low side mosfets. The four mosfets are arranged in a linear array, one next to the other. A typical four-mosfet package is 29×13×3.15 mm, has twenty pins including ten on each of the 29 mm sides, and the package configuration is known as a thin shrink small outline package (TSSOP) or a small outline integrated circuit SOIC). See FIG. 2. The package has several disadvantages. It is not only large but also has poor thermal/electrical performance and is expensive in its materials, including its lead frame and encapsulating material.